The present invention relates to an electrical junction box for use with electrical wiring for an automobile or the like, and more particularly to a structure of the electrical junction box which may prevent short circuits of bus bars located in the electrical junction box due to water entering the electrical junction box.
FIG. 4 is an exploded perspective view of a conventional electrical junction box constructed of an upper cases 4, a lower case 5 and a wiring board assembly 3 to be received in the upper case 4 and the lower case 5. The wiring board assembly 3 is constructed of a first bus bar set 10 including a plurality of bus bars 10A, 10B, 10C and 10D, a second bus bar set 1 including a plurality of bus bars 1A, 1B and 1C, and an insulating board 2 to be interposed between the first bus bar set 10 and the second bus bar set 1. The upper case 4 and the lower case 5 are formed with a plurality of connector housings 6 and 6' for connecting a fuse, relay, wire harness or the like (not shown) to the bus bar sets 10 and 1, respectively. The connector housing 6 and 6' are formed with a plurality of connection holes 6a and 6'a for receiving tab terminals 10a and 1a of the bus bar sets 10 and 1, respectively. Further, the upper case 4 and the lower case 5 are formed with a plurality of crossing ribs 7 and 7', respectively.
FIG. 5 is a sectional view of a part of the electrical junction box under the assembled condition, and FIG. 6 is a cross section taken along the line VI--VI in FIG. 5. As shown in FIGS. 5 and 6, the wiring board assembly 3 comprised of the first and second bus bar sets 10 and 1 and the insulating board 2 is sandwiched between the upper and lower ribs 7 and 7' of the upper and lower cases 4 and 5. The ribs 7 and 7' serve to increase a mechanical strength of the upper and lower cases 4 and 5, and also serve to reliably fix the first and second bus bar sets 10 and 1 in a predetermined position. The insulating board 2 is formed on its opposite surfaces with pattern projections 2a corresponding to patterns of the bus bar sets 10 and 1, so that a plurality of grooves 2b are formed to receive the bus bars 10A to 10D of the bus bar set 10 and the bus bars 1A to 1C of the bus bar set 1.
A waterproof cover (not shown) is usually mounted on the upper case 4 by a locking means, so as to prevent entry of water into the electrical junction box. However, when a vehicle is washed with water under a high pressure, for example, the water tends to enter the electrical junction box through the locking means of the waterproof cover. As shown in FIGS. 5 and 6, the water having entered the electrical junction box tends to stay at a contact portion between the first bus bar set 10 and the rib 7 and a contact portion between the second bus bar set 1 and the rib 7' as depicted by W. Such stay of the water W causes the generation of leak current between the adjacent bus bars 10A and 10B, for example, or between the opposite bus bars 10A and 1A, for example. As a result, the electrical parts such as a relay connected to the bus bars will malfunction. Further, as the wiring board assembly 3 is enclosed by the ribs 7 and 7', the water W cannot flow out of the spaces between the wiring board assembly 3 and the ribs 7 and 7', causing the generating of corrosion of the bus bars. Further, the staying water W will be moved or scattered in the spaces due to vibration of the automobile to cause the generation of leak current between the other bus bars.